1. Field of the Invention
The present invention relates to a photosensitive polymer and a chemically amplified resist composition, and more particularly, to a fluorine-containing photosensitive polymer and a resist composition including the photosensitive polymer.
2. Description of the Related Art
As the manufacture of semiconductor devices becomes complicated and the integration density of semiconductor devices increases, there is a need to form a fine pattern. Furthermore, with regard to semiconductor devices of 1-Gigabit or greater, a pattern size having a design rule of 0.1 xcexcm or less is needed. However, when a conventional photoresist material is exposed with KrF excimer laser (248 nm), there is a limitation in forming such fine patterns. For this reason, a lithography technique using a new exposure light source, ArF excimer laser (193 nm), has emerged, and the focus of the research on ArF resist compositions has been on acrylic polymers and COMAs (cycloolefin-maleic anhydrides).
For a smaller pattern size, there is extensive focus on lithography using short-wavelength generating F2 (157 nm) excimer laser. Conventional KrF or ArF resists are unsuitable for use with the short-wavelength source of 157 nm due to their low transmittance. Therefore, a polymer with a novel structure which is transparent to a157-nm wavelength is more suitable. A chemical component dissolvable in developer includes phenol, carboxylic acid, xcex1-fluorocarbon-substituted alcohol, and hydroxy silane having a structure of formula 1 below: 
Among these components, phenol and carboxylic acid have a very poor transmittance with respect to 157-nm beam. Whereas xcex1-fluorocarbon-substituted methanol and hydroxy silane are relatively more transparent at a wavelength of 157-nm. As a result, interest in studying xcex1-fluorocarbon-substituted methanol and hydroxy silane has increased.
According to recent research data, appropriate substitution of a phenolic or carboxylic derivative with fluorine is found to be effective for transmittance and contrast enhancement, suggesting its use as a polymer for a 157-nm exposure source (Journal of Photopolymer Science and Technology, Vol. 14, No. 4, 583-593, 2001; Journal of Photopolymer Science and Technology, Vol. 14, No. 4, 669-674, 2001).
Structures of fluorine-substituted photosensitive polymers for conventional resist compositions are shown in formula 2 below. 
Despite the existence of the ether group in those structures of formula 2 above, advantages of a high transmittance due to the acrylate polymer and of their ease of preparation has increased use of those structures substituted with fluorocarbon to an appropriate degree. t-butyl trifluoromethyl acrylate is widely used as a monomer for enhancing contrast. An aromatic hydrocarbon monomer having a low transmittance at 157-nm can be changed into a hexafluoroisopropanol-substituted styrene structure with enhanced transmittance to be suitable as a resist material.
In addition, extensive research into resist compositions derived from acrylate polymers, non-carboxylic fluorinated vinyl ether polymers, and polymers with cyclic ether in their main chain, and copolymers of tetrafluoroethylene and norbornene derivatives known to be highly transparent at 157-nm, having structures of formula 3 below, are in progress. 
In formula 3 above, R may be a methyl group, a t-butyl group, an adamantly group, a trifluoromethylnorbornyl group, or a hexafluoroisopropyl group.
A fluorinated polymer has excellent transmittance at 157-nm when it contains more fluorine atoms, but its enhanced hydrophobicity degrades adhesion to an underlayer. To date, resist materials having a suitable structure for 157-nm laser have not been found. Therefore, there is a need for a polymer having a high transmittance at 157-nm and without the aforementioned problems and thus be suitable as a resist material for F2 excimer laser.
It is an object of the present invention to provide a photosensitive polymer having a structure to give a high transmittance at a F2 excimer laser wavelength of 157 nm and good adhesion to an underlayer.
It is another object of the present invention to provide a resist composition allowing development with conventional developers and having a high transmittance at a F2 excimer laser wavelength of 157 nm, good hydrophilicity, and good adhesion to an underlayer.
According to an aspect of the present invention, a photosensitive polymer is provided having an average molecular weight of about 3,000-100,000 with a repeating unit including a group of one of the structures of formula 4 below: 
In the photosensitive polymer, the repeating unit may have a structure of formula 5 below: 
where n is 0 or 1, and R1 is a substituted or unsubstituted C1-C5 hydrocarbon group.
The repeating unit of formula 5 above may be derived from a monomer of formula 6 below: 
Alternatively, the repeating unit constituting the photosensitive polymer according to an embodiment of the present invention may have a structure of formula 7 below: 
where n is 0 or 1, and R2 is a substituted or unsubstituted C1-C5 hydrocarbon group.
The repeating unit of formula 7 above may be derived from a monomer of formula 8 below: 
Alternatively, the repeating unit constituting the photosensitive polymer according to an embodiment of the present invention may have a structure of formula 9 below: 
where n is 0 or 1, and R3 is a substituted or unsubstituted C1-C5 hydrocarbon group.
The repeating unit of formula 9 above may be derived from a monomer of formula 10 below: 
Alternatively, the repeating unit constituting the photosensitive polymer according to an embodiment of the present invention may have a structure of formula 11 below: 
where R4 is a substituted or unsubstituted C1-C5 hydrocarbon group.
The repeating unit of formula 11 above may be derived from a monomer of formula 12 below: 
Alternatively, the repeating unit constituting the photosensitive polymer according to an embodiment of the present invention may have a structure of formula 13 below: 
The repeating unit of formula 13 above may be derived from a monomer of formula 14 below: 
According to a second embodiment of the present invention, a photosensitive polymer is provided having an average molecular weight of about 3,000-100,000 with a first repeating unit having one group of a structure selected from formula 4 above and at least one second repeating unit selected from the group consisting of acrylate, methacrylate, maleic anhydride, norbornene, styrene, tetrafluoroethylene, and sulfur dioxide derivatives.
Alternatively, the photosensitive polymer according to the second embodiment of the present invention may have a structure of formula 15 below: 
where n is 0 or 1; R1 is a substituted or unsubstituted C1-C5 a hydrocarbon group; R5 is hydrogen atom, a methyl group, or a trifluoromethyl group; R6 is a hydrogen atom or a substituted or unsubstituted C1-C20 hydrocarbon group; and R7 is hydrogen atom, a hydroxyl group, a nitrile group, a substituted or unsubstituted C1-C12 alkyl group, a fluorinated C1-C12 alkyl group, an alkoxy group, or an ester group. Preferably, R6 is a C4-C12 acid-labile group, and more preferably, a t-butyl group. Preferably, R7 is a fluorinated C3-C12 alkyl alcohol group or an acid-labile C4-C12 ester group. For example, R7 may be a 2-hydroxyhexafluoroisopropyl group, a t-butoxycarbonyloxyhexafluoroisopropyl group, or a 2-hydroxytrifluoroisopropyl group.
Alternatively, the photosensitive polymer according to the second embodiment of the present invention may have a structure of formula 16 below: 
where n is 0 or 1; R2 is a substituted or unsubstituted C1-C5 hydrocarbon group; R5 a is hydrogen atom, a methyl group, or a trifluoromethyl group; R6 is a hydrogen atom or a substituted or unsubstituted C1-C20 hydrocarbon group; and R8 is a hydrogen atom, a hydroxyl group, a nitrile group, a substituted or unsubstituted C1-C12 alkyl group, a fluorinated C1-C12 alkyl group, an alkoxy group, or an ester group. Preferably, R6 is a C4-C12 acid-labile group, and more preferably, a t-butyl group. Preferably, R8 is a fluorinated C3-C10 alkyl alcohol group. For example, R8 may be a 2-hydroxyhexafluoroisopropyl group.
Alternatively, the photosensitive polymer according to the second embodiment of the present invention may have a structure of formula 17 below: 
where n is 0 or 1; R2 is a substituted or unsubstituted C1-C5 hydrocarbon group; R5 is a hydrogen atom, a methyl group, or a trifluoromethyl group; R6 is a hydrogen atom or a substituted or unsubstituted C1-C20 hydrocarbon group; and R7 is a hydrogen atom, a hydroxyl group, a nitrile group, a substituted or unsubstituted C1-C12 alkyl group, a fluorinated C1-C12 alkyl group, an alkoxy group, or an ester group. Preferably, R6 is a C4-C12 acid-labile group, and more preferably, a t-butyl group. Preferably, R7 is a fluorinated C3-C10 alkyl alcohol group or an acid-labile C4-C12 ester group. For example, R7 may be a 2-hydroxyhexafluoroisopropyl group, a t-butoxycarbonyloxyhexafluoroisopropyl group, or a 2-hydroxytrifluoroisopropyl group.
Alternatively, the photosensitive polymer according to the second embodiment of the present invention may have a structure of formula 18 below: 
where n is 0 or 1; R2 is a substituted or unsubstituted C1-C5 hydrocarbon group; R5 and R9, independent of one another, may be a hydrogen atom, a methyl group, or a trifluoromethyl group; R6 and R10, independent of one another, may be a hydrogen atom or a substituted or unsubstituted C1-C20 hydrocarbon group; and R7 is a hydrogen atom, a hydroxyl group, a nitrile group, a substituted or unsubstituted C1-C12 alkyl group, a fluorinated C1-C12 alkyl group, an alkoxy group, or an ester group. Preferably, either R6 or R10 is a C4-C12 acid-labile group, and more preferably, a t-butyl group. Preferably, R7 is a fluorinated C3-C10 alkyl alcohol group or an acid-labile C4-C12 ester group. For example, R7 may be a 2-hydroxyhexafluoroisopropyl group, a t-butoxycarbonyloxyhexafluoroisopropyl group, or a 2-hydroxytrifluoroisopropyl group.
Alternatively, the photosensitive polymer according to the second embodiment of the present invention may have a structure of formula 19 below: 
where n is 0 or 1; R3 is a substituted or unsubstituted C1-C5 hydrocarbon group; R5 is a hydrogen atom, a methyl group, or a trifluoromethyl group; R6 is a hydrogen atom or a substituted or unsubstituted C1-C20 hydrocarbon group; and R7 is a hydrogen atom, a hydroxyl group, a nitrile group, a substituted or unsubstituted C1-C12 alkyl group, a fluorinated C1-C12 alkyl group, an alkoxy group, or an ester group. Preferably, R6 is a C4-C12 acid-labile group, and more preferably, a t-butyl group. Preferably, R7 is a fluorinated C3-C10 alkyl alcohol group or an acid-labile C4-C12 ester group. For example, R7 may be a 2-hydroxyhexafluoroisopropyl group, a t-butoxycarbonyloxyhexafluoroisopropyl group, or a 2-hydroxytrifluoroisopropyl group.
Alternatively, the photosensitive polymer according to the second embodiment of the present invention may have a structure of formula 20 below: 
where R4 is a substituted or unsubstituted C1-C5 hydrocarbon group; R5 is a hydrogen atom, a methyl group, or a trifluoromethyl group; and R6 is a hydrogen atom or a substituted or unsubstituted C1-C20 hydrocarbon group. Preferably, R6 is a C4-C12acid-labile group, and more preferably, a t-butyl group.
Alternatively, the photosensitive polymer according to the second embodiment of the present invention may have a structure of formula 21 below: 
where R5 is a hydrogen atom, a methyl group, or a trifluoromethyl group; and R6 is a hydrogen atom or a substituted or unsubstituted C1-C20 hydrocarbon group. Preferably, R6 is a C4-C12 acid-labile group, and more preferably, a t-butyl group.
Alternatively, the photosensitive polymer according to the second embodiment of the present invention may have a structure of formula 22 below: 
where R5 is a hydrogen atom, a methyl group, or a trifluoromethyl group; R6 is a hydrogen atom or a substituted or unsubstituted C1-C20 hydrocarbon group; and R8 is a hydrogen atom, a hydroxyl group, a nitrile group, a substituted or unsubstituted C1-C12 alkyl group, a fluorinated C1-C12 alkyl group, an alkoxy group, or an ester group. Preferably, R6 is a C4-C12 acid-labile group, and more preferably, a t-butyl group. Preferably, R8 is a fluorinated C3-C10 alkyl alcohol group. For example, R8 may be a 2-hydroxyhexafluoroisopropyl group.
According to another aspect of the present invention, there is provided a resist composition comprising the photosensitive polymer having one structure of the formulae above and a photoacid generator (PAG).
Preferably, the photoacid generator is contained in an amount of about 1-15% by weight based on the total weight of the photosensitive polymer. Preferably, the photoacid generator comprises triarylsulfonium salts, diaryliodonium salts, sulfonates, or a mixture of these compounds. Suitable examples of the photoacid generator include triphenylsulfonium triflate, triphenylsulfonium antimonate, diphenyliodonium triflate, diphenyliodonium antimonite, methoxydiphenyliodonium triflate, di-t-butyldiphenyliodonium triflate, 2,6-dinitrobenzyl sulfonates, pyrogallol tris(alkylsulfonates), N-hydroxysuccinimide triflate, norbornene-dicarboximide-triflate, triphenylsulfonium nonaflate, diphenyliodonium nonaflate, methoxydiphenyliodonium nonaflate, di-t-butyldiphenyliodonium nonaflate, N-hydroxysuccinimide nonaflate, norbornene-dicarboximide-nonaflate, triphenylsulfonium perfluorooctanesulfonate (PFOS), diphenyliodonium perfluorooctanesulfonate, methoxydiphenyliodonium perfluorooctanesulfonate, di-t-butyldiphenyliodonium triflate, N-hydroxysuccinimide perfluorooctanesulfonate, norbornene-dicarboximide perfluorooctanesulfonate, or a mixture of these compounds.
It is preferable that the resist composition according to an embodiment of the present invention further comprises an organic base. In this case, the organic base may be contained in an amount of about 0.01-2.0% by weight based on the total weight of the photosensitive polymer. Preferably, the organic base comprises a single tertiary amine compound or a mixture of at least two ternary amine compounds. For example, the organic base may be triethylamine, triisobutylamine, triisooctylamine, triisodecylamine, diethanolamine, triethanolamine, or a mixture of these compounds.
It is preferable that the resist composition according to an embodiment of the present invention further comprises a surfactant of about 30-200 ppm.
It is preferable that the resist composition according to an embodiment of the present invention further comprises a dissolution inhibitor of about 0.1-50% by weight based on the total weight of the photosensitive polymer.
A photosensitive polymer according to an embodiment of the present invention contains relatively more fluorine atoms and has a hydrate structure with a number of hydrophilic groups, for example, hydroxyl groups. Thus, a resist composition derived from the polysensitive polymer according to the present invention provides good adhesion to an underlayer and high transmittance at a F2 excimer laser wavelength of 157 nm. The photosensitive polymer according to an embodiment of the present invention has an appropriate glass transition temperature in the range of about 120-180xc2x0 C., and the resist composition according to the present invention derived from the photosensitive polymer allows development using conventional developers. Therefore, the resist composition according to the present invention shows excellent lithography performance when applied to a photolithography process using a F2 excimer laser of 157 nm, and thus is expected to be useful in the manufacture of next generation semiconductor devices.